Impact of influenza B lineage-level mismatch between trivalent seasonal influenza vaccines and circulating viruses, 1999-2012

One HA stalk topping multiple heads as a novel influenza vaccine

Classic chimeric hemagglutinin (cHA) was designed to induce immune responses against the conserved stalk domain of HA. However, it is unclear whether combining more than one HA head domain onto one stalk domain is immunogenic and further induce immune responses against influenza viruses. Here, we constructed numerous novel cHAs comprising two or three fuzed head domains from different subtypes grafted onto one stalk domain, designated as cH1-H3, cH1-H7, cH1-H3-H7, and cH1-H7-H3. The three-dimensional structures of these novel cHAs were modelled using bioinformatics simulations. Structural analysis showed that the intact neutralizing epitopes were exposed in cH1-H7 and were predicted to be immunogenic. The immunogenicity of the cHAs constructs was evaluated in mice using a chimpanzee adenoviral vector (AdC68) vaccine platform. The results demonstrated that cH1-H7 expressed by AdC68 (AdC68-cH1-H7) induced the production of high levels of binding antibodies, neutralizing antibodies, and hemagglutinin inhibition antibodies against homologous pandemic H1N1, drifted seasonal H1N1, and H7N9 virus. Moreover, vaccinated mice were fully protected from a lethal challenge with the aforementioned influenza viruses. Hence, cH1-H7 cHAs with potent immunogenicity might be a potential novel vaccine to provide protection against different subtypes of influenza virus.

Preclinical evaluation of a universal inactivated influenza B vaccine based on the mosaic hemagglutinin-approach

We have developed a new universal influenza B vaccination strategy based on inactivated influenza B viruses displaying mosaic hemagglutinins (mHAs). Recombinant mHA viruses were constructed by replacing the four major antigenic sites of influenza B virus HAs, with those from exotic avian influenza A virus HAs. Sequential vaccination of naïve mice with mHA-based vaccines elicited higher immune responses towards the immuno-subdominant conserved epitopes of the HA than vaccination with wildtype viruses. Among the different preparations tested, mHA split vaccines were less immunogenic than their whole inactivated virus counterparts. This lower immunogenicity was overcome by the combination with adjuvants. mHA split vaccines adjuvanted with a Toll-like receptor-9 agonist (CpG 1018) increased Th1 immunity and in vivo cross-protection, whereas adjuvanting with an MF59-like oil-in-water nano-emulsion (AddaVax) enhanced and broadened humoral immune responses and antibody-mediated cross-protection. The mHA vaccines with or without adjuvant were subsequently evaluated in mice that were previously immunized to closely mimic human pre-existing immunity to influenza B viruses and the contribution of innate and cellular immunity was evaluated in this model. We believe these preclinical studies using the mHA strategy represent a major step toward the evaluation of a universal influenza B virus vaccine in clinical trials.

Antigenic analysis of the influenza B virus hemagglutinin protein

Influenza B viruses (IBVs) primarily infect humans and are a common cause of respiratory infections in humans. Here, to systematically analyze the antigenicity of the IBVs Hemagglutinin (HA) protein, 31 ​B/Victoria and 19 ​B/Yamagata representative circulating strains were selected from Global Initiative of Sharing All Influenza Data (GISAID), and pseudotyped viruses were constructed with the vesicular stomatitis virus system. Guinea pigs were immunized with three doses of vaccines (one dose of DNA vaccines following two doses of pseudotyped virus vaccines) of the seven IBV vaccine strains, and neutralizing antibodies against the pseudotyped viruses were tested. By comparing differences between various vaccine strains, we constructed several pseudotyped viruses that contained various mutations based on vaccine strain BV-21. The vaccine strains showed good neutralization levels against the epidemic virus strains of the same year, with neutralization titers ranging from 370 to 840, while the level of neutralization against viruses prevalent in previous years decreased 1-10-fold. Each of the high-frequency epidemic strains of B/Victoria and B/Yamagata not only induced high neutralizing titers, but also had broadly neutralizing effects against virus strains of different years, with neutralizing titers ranging from 1000 to 7200. R141G, D197 ​N, and R203K were identified as affecting the antigenicity of IBV. These mutation sites provide valuable references for the selection and design of a universal IBV vaccine strain in the future.

Genetic Reassortment in a Child Coinfected with Two Influenza B Viruses, B/Yamagata Lineage and B/Victoria-Lineage Strains

We identified a child coinfected with influenza B viruses of B/Yamagata and B/Victoria lineages, in whom we analyzed the occurrence of genetic reassortment. Plaque purification was performed using a throat swab specimen from a 9-year-old child, resulting in 34 well-isolated plaques. The genomic composition of eight gene segments (HA, NA, PB1, PB2, PA, NP, M, and NS genes) for each plaque was determined at the lineage level. Of the 34 plaques, 21 (61.8%) had B/Phuket/3073/2013 (B/Yamagata)-like sequences in all gene segments, while the other 13 (38.2%) were reassortants with B/Texas/02/2013 (B/Victoria)-like sequences in 1-5 of the 8 segments. The PB1 segment had the most B/Victoria lineage genes (23.5%; 8 of 34 plaques), while PB2 and PA had the least (2.9%; 1 of 34 plaques). Reassortants with B/Victoria lineage genes in 2-5 segments showed the same level of growth as viruses with B/Yamagata lineage genes in all segments. However, reassortants with B/Victoria lineage genes only in the NA, PB1, NP, or NS segments exhibited reduced or undetectable growth. We demonstrated that various gene reassortments occurred in a child. These results suggest that simultaneous outbreaks of two influenza B virus lineages increase genetic diversity and could promote the emergence of new epidemic strains.

Impact of sex on humoral immunity with live influenza B virus vaccines in mice

Influenza B virus (FLUBV) poses a significant infectious threat, with frequent vaccine mismatch limiting its effectiveness. Our previous work investigated the safety and efficacy of modified live attenuated FLUBV vaccines with rearranged genomes (FluB-RAM and FluB-RANS) or a temperature-sensitive PB1 segment with a C-terminal HA tag (FluB-att). In this study, we compared the immune responses of female and male DBA/2J mice vaccinated with these vaccines, including versions containing a chimeric HA segment with an N-terminal IgA-inducing peptide (IGIP). Importantly, both recombinant viruses with and without IGIP remained genetically stable during egg passage. We found that introducing IGIP strengthened vaccine attenuation, particularly for FluB-RAM/IGIP. Prime-boost vaccination completely protected mice against lethal challenge with a homologous FLUBV strain. Notably, recombinant viruses induced robust neutralizing antibody responses (hemagglutination inhibition titers ≥40) alongside antibodies against NA and NP. Interestingly, female mice displayed a consistent trend of enhanced humoral and cross-reactive IgG and IgA responses against HA, NA, and NP compared to male counterparts, regardless of the vaccine used. However, the presence of IGIP generally led to lower anti-HA responses but higher anti-NA and anti-NP responses, particularly of the IgA isotype. These trends were further reflected in mucosal and serological responses two weeks after challenge, with clear distinctions based on sex, vaccine backbone, and IGIP inclusion. These findings hold significant promise for advancing the development of universal influenza vaccines.

Unlocking the Power of Influenza Vaccines for Pediatric Population: A Narrative Review

The flu, often known as influenza, is a dangerous public health hazard for the pediatric population. Immunization is essential for decreasing the burden of the disease and avoiding complications related to influenza. However, the immunogenicity, efficacy, and safety of different influenza vaccines in children warrant careful evaluation. The purpose of this narrative review is to give a summary of the existing literature on the immunogenicity, efficacy, and safety of several vaccinations against influenza viruses in children. The review incorporates evidence from a range of studies focusing on the outcomes of interest. Immunogenicity studies have shown that influenza vaccines induce a robust immune response in children, primarily through neutralizing antibodies' formation. However, variations in vaccine composition influence the duration and magnitude of immune responses. Safety is a crucial consideration in pediatric vaccination. In children, influenza vaccinations have generally shown a high safety profile, with mild and temporary side effects being the most common. Vaccinations against influenza have shown a modest level of efficacy in avoiding hospitalizations linked to influenza, laboratory-confirmed influenza infections, and serious consequences in children. Live attenuated vaccines have shown higher effectiveness against matched strains compared to inactivated vaccines. In conclusion, this narrative review highlights that receiving influenza vaccination in children aged six to 47 months is very important. While different vaccines exhibit varying immunogenicity, safety profiles, and effectiveness, they all contribute to reducing the burden of influenza among children. Future research should focus on optimizing vaccine strategies, improving vaccine coverage, and evaluating long-term protection.

A potential Chinese medicine monomer against influenza A virus and influenza B virus: isoquercitrin

BACKGROUND

Influenza viruses, especially Influenza A virus and Influenza B virus, are respiratory pathogens and can cause seasonal epidemics and pandemics. Severe influenza viruses infection induces strong host-defense response and excessive inflammatory response, resulting in acute lung damage, multiple organ failure and high mortality. Isoquercitrin is a Chinese medicine monomer, which was reported to have multiple biological activities, including antiviral activity against HSV, IAV, SARS-CoV-2 and so on. Aims of this study were to assess the in vitro anti-IAV and anti-IBV activity, evaluate the in vivo protective efficacy against lethal infection of the influenza virus and searched for the more optimal method of drug administration of isoquercitrin.

METHODS

In vitro infection model (MDCK and A549 cells) and mouse lethal infection model of Influenza A virus and Influenza B virus were used to evaluate the antiviral activity of isoquercitrin.

RESULTS

Isoquercitrin could significantly suppress the replication in vitro and in vivo and reduced the mortality of mouse lethal infection models. Compared with virus infection group, isoquercitrin mitigated lung and multiple organ damage. Moreover, isoquercitrin blocked hyperproduction of cytokines induced by virus infection via inactivating NF-κB signaling. Among these routes of isoquercitrin administration, intramuscular injection is a better drug delivery method.

CONCLUSION

Isoquercitrin is a potential Chinese medicine monomer Against Influenza A Virus and Influenza B Virus infection.

Self-amplifying mRNA seasonal influenza vaccines elicit mouse neutralizing antibody and cell-mediated immunity and protect ferrets

Currently licensed influenza vaccines focus immune responses on viral hemagglutinin (HA), while the other major surface glycoprotein neuraminidase (NA) is not tightly controlled in inactivated vaccine formulations despite evidence that anti-NA antibodies reduce clinical disease. We utilized a bicistronic self-amplifying mRNA (sa-mRNA) platform encoding both HA and NA from four seasonal influenza strains, creating a quadrivalent influenza vaccine. sa-mRNA vaccines encoding an NA component induced the production of NA-inhibiting antibodies and CD4+ T-cell responses in both monovalent and quadrivalent formulations. Including NA in the vaccine enabled cross-neutralization against antigenically drifted strains and provided greater protection than HA alone upon A(H3N2) challenge in ferrets. These results demonstrate that next-generation bicistronic sa-mRNA vaccines expressing HA and NA induce potent antibodies against both viral coat proteins, as well as vaccine-specific cell-mediated immunity. When formulated as a quadrivalent seasonal influenza vaccine, the sa-mRNA platform provides an opportunity to increase the breadth of protection through cross-neutralizing anti-NA antibodies.

Antigenic Landscape Analysis of Individuals Vaccinated with a Universal Influenza Virus Vaccine Candidate Reveals Induction of Cross-Subtype Immunity

Current influenza virus vaccines have to be closely matched to circulating strains to provide good protection, and antigenic drift and emerging pandemic influenza virus strains present a difficult challenge for them. Universal influenza virus vaccines, including chimeric hemagglutinin (cHA)-based constructs that target the conserved stalk domain of hemagglutinin, are in clinical development. Due to the conservation of the stalk domain, antibodies directed to it show broad binding profiles, usually within group 1 and group 2 influenza A or influenza B virus phylogenies. However, determining the binding breadth of these antibodies with commonly used immunological methods can be challenging. Here, we analyzed serum samples from a phase I clinical trial (CVIA057, NCT03300050) using an influenza virus protein microarray (IVPM). The IVPM technology allowed us to assess immune responses not only to a large number of group 1 hemagglutinins but also group 2 and influenza B virus hemagglutinins. In CVIA057, different vaccine modalities, including a live attenuated influenza virus vaccine and inactivated influenza virus vaccines with or without adjuvant, all in the context of cHA constructs, were tested. We found that vaccination with adjuvanted, inactivated vaccines induced a very broad antibody response covering group 1 hemagglutinins, with limited induction of antibodies to group 2 hemagglutinins. Our data show that cHA constructs do indeed induce very broad immune responses and that the IVPM technology is a useful tool to measure this breadth that broadly protective or universal influenza virus vaccines aim to induce. IMPORTANCE The development of a universal influenza virus vaccine that protects against seasonal drifted, zoonotic, or emerging pandemic influenza viruses would be an extremely useful public health tool. Here, we test a technology designed to measure the breadth of antibody responses induced by this new class of vaccines.

A prophylactic effect of aluminium-based adjuvants against respiratory viruses via priming local innate immunity

Infection caused by respiratory viruses can lead to a severe respiratory disease and even death. Vaccination is the most effective way to prevent the disease, but it cannot be quickly applied when facing an emerging infectious disease. Here, we demonstrated that immunization with an aluminium-zinc hybrid particulate adjuvant (FH-001) alone, bearing great resemblance in morphology with commonly used aluminium-based adjuvants in vaccines, could quickly induce mice to generate a broadly protective immune response to resist the lethal challenge of influenza B viruses. Furthermore, a multi-omics-based analysis revealed that the alveolar macrophage and type I interferon pathway, rather than adaptive immunity and type II interferon pathway, were essential for the observed prophylactic effect of FH-001. More importantly, a similar protective effect was observed against influenza A virus strain A/Shanghai/02/2013(H7N9), A/California/04/2009(H1N1) and respiratory syncytial virus. Therefore, we introduced here a new and promising strategy that can be quickly applied during the outbreak of emerging respiratory viruses.

Molecular characterization and evolution dynamics of influenza B viruses circulating in Germany from season 1996/1997 to 2019/2020

Influenza B viruses are responsible for significant disease burden caused by viruses of both the Yamagata- and Victoria-lineage. Since the circulating patterns of influenza B viruses in different countries vary we investigated molecular properties and evolution dynamics of influenza B viruses circulating in Germany between 1996 and 2020. A change of the dominant lineage occurred in Germany in seven seasons in over past 25 years. A total of 676 sequences of hemagglutinin coding domain 1 (HA1) and 516 sequences of neuraminidase (NA) genes of Yamagata- and Victoria-lineage viruses were analyzed using time-scaled phylogenetic tree. Phylogenetic analysis demonstrated that Yamagata-lineage viruses are more diverse than the Victoria-lineage viruses and could be divided into nine genetic groups whereas Victoria-lineage viruses presented six genetic groups. Comparative phylogenetic analyses of both the HA and NA segments together revealed a number of inter-lineage as well as inter- and intra-clade reassortants. We identified key amino acid substitutions in major HA epitopes such as in four antigenic sites and receptor-binding sites (RBS) and in the regions close to them, with most substitutions in the 120-loop of both lineage viruses. Altogether, seventeen substitutions were fixed over time within the Yamagata-lineage with twelve of them in the antigenic sites. Thirteen substitutions were identified within the Victoria-lineage, with eleven of them in the antigenic sites. Moreover, all Victoria-lineage viruses of the 2017/2018 season were characterized by a deletion of two amino acids at the position 162-163 in the antigenic site of HA1. The viruses with triple deletion Δ162-164 were found in Germany since season 2018/2019. We highlighted the interplay between substitutions in the glycosylation sites and RBS and antigenic epitope during HA evolution. The results obtained underscore the need for continuous monitoring of circulating influenza B viruses. Early detection of strains with genetic and antigenic variation is essential to predict the circulation patterns for the following season. Such information is important for the development of optimal vaccines and strategies for prevention and control of influenza.

Substitutions near the HA receptor binding site explain the origin and major antigenic change of the B/Victoria and B/Yamagata lineages

Influenza B virus primarily infects humans, causing seasonal epidemics globally. Two antigenic variants-Victoria-like and Yamagata-like-were detected in the 1980s, of which the molecular basis of emergence is still incompletely understood. Here, the antigenic properties of a unique collection of historical virus isolates, sampled from 1962 to 2000 and passaged exclusively in mammalian cells to preserve antigenic properties, were determined with the hemagglutination inhibition assay and an antigenic map was built to quantify and visualize the divergence of the lineages. The antigenic map revealed only three distinct antigenic clusters-Early, Victoria, and Yamagata-with relatively little antigenic diversity in each cluster until 2000. Viruses with Victoria-like antigenic properties emerged around 1972 and diversified subsequently into two genetic lineages. Viruses with Yamagata-like antigenic properties evolved from one lineage and became clearly antigenically distinct from the Victoria-like viruses around 1988. Recombinant mutant viruses were tested to show that insertions and deletions (indels), as observed frequently in influenza B virus hemagglutinin, had little effect on antigenic properties. In contrast, amino-acid substitutions at positions 148, 149, 150, and 203, adjacent to the hemagglutinin receptor binding site, determined the main antigenic differences between the Early, Victoria-like, and Yamagata-like viruses. Surprisingly, substitutions at two of the four positions reverted in recent viruses of the Victoria lineage, resulting in antigenic properties similar to viruses circulating ∼50 y earlier. These data shed light on the antigenic diversification of influenza viruses and suggest there may be limits to the antigenic evolution of influenza B virus.

Impact of adjuvant: Trivalent vaccine with quadrivalent-like protection against heterologous Yamagata-lineage influenza B virus

As new vaccine technologies and platforms, such as nanoparticles and novel adjuvants, are developed to aid in the establishment of a universal influenza vaccine, studying traditional influenza split/subunit vaccines should not be overlooked. Commercially available vaccines are typically studied in terms of influenza A H1 and H3 viruses but influenza B viruses need to be examined as well. Thus, there is a need to both understand the limitations of split/subunit vaccines and develop strategies to overcome those limitations, particularly their ability to elicit cross-reactive antibodies to the co-circulating Victoria (B-V) and Yamagata (B-Y) lineages of human influenza B viruses. In this study, we compared three commercial influenza hemagglutinin (HA) split/subunit vaccines, one quadrivalent (H1, H3, B-V, B-Y HAs) and two trivalent (H1, H3, B-V HAs), to characterize potential differences in their antibody responses and protection against a B-Y challenge. We found that the trivalent adjuvanted vaccine Fluad, formulated without B-Y HA, was able to produce antibodies to B-Y (cross-lineage) on a similar level to those elicited from a quadrivalent vaccine (Flucelvax) containing both B-V and B-Y HAs. Interestingly, Fluad protected mice from a lethal cross-lineage B-Y viral challenge, while another trivalent vaccine, Fluzone HD, failed to elicit antibodies or full protection following challenge. Fluad immunization also diminished viral burden in the lungs compared to Fluzone and saline groups. The success of a trivalent vaccine to provide protection from a cross-lineage influenza B challenge, similar to a quadrivalent vaccine, suggests that further analysis of different split/subunit vaccine formulations could identify mechanisms for vaccines to target antigenically different viruses. Understanding how to increase the breadth of the immune response following immunization will be needed for universal influenza vaccine development.

A CpG 1018 adjuvanted neuraminidase vaccine provides robust protection from influenza virus challenge in mice

Influenza virus infections pose a significant threat to global health. Vaccination is the main countermeasure against influenza virus spread, however, the effectiveness of vaccines is variable. Current seasonal influenza virus vaccines mostly rely on the immunodominant hemagglutinin (HA) glycoprotein on the viral surface, which usually leads to a narrow and strain-specific immune response. The HA undergoes constant antigenic drift, which can lead to a dramatic loss in vaccine effectiveness, requiring the annual reformulation and readministration of influenza virus vaccines. Recently, it has been demonstrated that the subdominant glycoprotein, neuraminidase (NA), is an attractive target for vaccine development. Here, we tested a newly developed recombinant influenza virus N1 neuraminidase vaccine candidate, named N1-MPP, adjuvanted with CpG 1018, a TLR9 agonist. Additionally, N2-MPP and B-NA-MPP vaccine constructs have been generated to cover the range of influenza viruses that are seasonally circulating in humans. These constructs have been characterized in vitro and in vivo regarding their functionality and protective potential. Furthermore, a trivalent NA-MPP mix was tested. No antigenic competition between the individual NA constructs was detected. By adjuvating the recombinant protein constructs with CpG 1018 it was possible to induce a strong and robust immune response against the NA, which provided full protection against morbidity and mortality after high lethal challenges in vivo. This study provides important insights for the development of a broadly protective NA-based influenza virus vaccine candidate.

Cross-Protection Induced by Virus-like Particles Derived from the Influenza B Virus

The mismatch between the circulating influenza B virus (IBV) and the vaccine strain contributes to the rapid emergence of IBV infection cases throughout the globe, which necessitates the development of effective vaccines conferring broad protection. Here, we generated influenza B virus-like particle (VLP) vaccines expressing hemagglutinin, neuraminidase, or both antigens derived from the influenza B virus (B/Washington/02/2019 (B/Victoria lineage)-like virus, B/Phuket/3073/2013 (B/Yamagata lineage)-like virus. We found that irrespective of the derived antigen lineage, immunizing mice with the IBV VLPs significantly reduced lung viral loads, minimized bodyweight loss, and ensured 100% survival upon Victoria lineage virus B/Colorado/06/2017 challenge infection. These results were closely correlated with the vaccine-induced antibody responses and HI titer in sera, IgG, IgA antibody responses, CD4+ and CD8+ T cell responses, germinal center B cell responses, and inflammatory cytokine responses in the lungs. We conclude that hemagglutinin, neuraminidase, or both antigen-expressing VLPs derived from these influenza B viruses that were circulating during the 2020/21 season provide cross-protections against mismatched Victoria lineage virus (B/Colorado/06/2017) challenge infections.

Vaccine Mismatches, Viral Circulation, and Clinical Severity Patterns of Influenza B Victoria and Yamagata Infections in Brazil over the Decade 2010-2020: A Statistical and Phylogeny-Trait Analyses

Worldwide, infections by influenza viruses are considered a major public health challenge. In this study, influenza B vaccine mismatches and clinical aspects of Victoria and Yamagata infections in Brazil were assessed. Clinical samples were collected from patients suspected of influenza infection. In addition, sociodemographic, clinical, and epidemiological information were collected by the epidemiological surveillance teams. Influenza B lineages were determined by real-time RT-PCR and/or Sanger sequencing. In addition, putative phylogeny−trait associations were assessed by using the BaTS program after phylogenetic reconstruction by a Bayesian Markov Chain Monte Carlo method (BEAST software package). Over 2010−2020, B/Victoria and B/Yamagata-like lineages co-circulated in almost all seasonal epidemics, with B/Victoria predominance in most years. Vaccine mismatches between circulating viruses and the trivalent vaccine strains occurred in five of the eleven seasons (45.5%). No significant differences were identified in clinical presentation or disease severity caused by both strains, but subjects infected by B/Victoria-like viruses were significantly younger than their B/Yamagata-like counterparts (16.7 vs. 31.4 years, p < 0.001). This study contributes to a better understanding of the circulation patterns and clinical outcomes of B/Victoria- and B/Yamagata-like lineages in Brazil and advocate for the inclusion of a quadrivalent vaccine in the scope of the Brazilian National Immunization Program.

Epidemiological and virological surveillance of influenza viruses in China during 2020-2021

Background

During the coronavirus disease 2019 (COVID-19) pandemic, seasonal influenza activity declined globally and remained below previous seasonal levels, but intensified in China since 2021. Preventive measures to COVID-19 accompanied by different epidemic characteristics of influenza in different regions of the world. To better respond to influenza outbreaks under the COVID-19 pandemic, we analyzed the epidemiology, antigenic and genetic characteristics, and antiviral susceptibility of influenza viruses in the mainland of China during 2020–2021.

Methods

Respiratory specimens from influenza like illness cases were collected by sentinel hospitals and sent to network laboratories in Chinese National Influenza Surveillance Network. Antigenic mutation analysis of influenza virus isolates was performed by hemagglutination inhibition assay. Next-generation sequencing was used for genetic analyses. We also conducted molecular characterization and phylogenetic analysis of circulating influenza viruses. Viruses were tested for resistance to antiviral medications using phenotypic and/or sequence-based methods.

Results

In the mainland of China, influenza activity recovered in 2021 compared with that in 2020 and intensified during the traditional influenza winter season, but it did not exceed the peak in previous years. Almost all viruses isolated during the study period were of the B/Victoria lineage and were characterized by genetic diversity, with the subgroup 1A.3a.2 viruses currently predominated. 37.8% viruses tested were antigenically similar to reference viruses representing the components of the vaccine for the 2020–2021 and 2021–2022 Northern Hemisphere influenza seasons. In addition, China has a unique subgroup of 1A.3a.1 viruses. All viruses tested were sensitive to neuraminidase inhibitors and endonuclease inhibitors, except two B/Victoria lineage viruses identified to have reduced sensitivity to neuraminidase inhibitors.

Conclusions

Influenza activity increased in the mainland of China in 2021, and caused flu season in the winter of 2021–2022. Although the diversity of influenza (sub)type decreases, B/Victoria lineage viruses show increased genetic and antigenic diversity. The world needs to be fully prepared for the co-epidemic of influenza and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus globally.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40249-022-01002-x.

Universal antibody targeting the highly conserved fusion peptide provides cross-protection in mice

Influenza is a major public health concern causing millions of hospitalizations every year. The current vaccines need annual updating based on prediction of likely strains in the upcoming season. However, mismatches between vaccines and the actual circulating viruses can occur, reducing vaccine effectiveness significantly because of the remarkably high rate of mutation in the viral glycoprotein, hemagglutinin (HA). Clearly, it would be of great interest to determine the potential role of universally conserved epitopes in inducing protective immunity. Here, an antibody against the 14-aa fusion peptide sequence at the N-terminus of the HA2 subunit (Uni-1) was investigated for its ability to elicit antibody-dependent cellular cytotoxicity (ADCC) in vitro and cross-protection against lethal infection in animals. Uni-1, known to neutralize influenza type A (IAV) in vitro, was found to induce strong ADCC against diverse influenza viruses, including human and avian IAVs and both lineages of type B (IBV). The ADCC effects against human IAVs by Uni-1 was comparable to ADCC induced by well-characterized antibodies, F10 and FI6V3. Importantly, mice treated with Uni-1 were protected against lethal challenge of IAV and IBV. These results revealed the versatile effector functions of this universal antibody against markedly diverse strains of both IAV and IBV.

The fusion peptide is the only universally conserved epitope in both IAV and IBV

Mono-specific universal antibody induces strong ADCC against human and avian IAV

Mono-specific universal antibody induces strong ADCC against IBV from both genetic lineages of IBV

The antibody has bi-functional effector functions against several influenza viruses

Influenza B: Prospects for the Development of Cross-Protective Vaccines

In this review, we analyze the epidemiological and ecological features of influenza B, one of the most common and severe respiratory infections. The review presents various strategies for cross-protective influenza B vaccine development, including recombinant viruses, virus-like particles, and recombinant proteins. We provide an overview of viral proteins as cross-protective vaccine targets, along with other updated broadly protective vaccine strategies. The importance of developing such vaccines lies not only in influenza B prevention, but also in the very attractive prospect of eradicating the influenza B virus in the human population.

Epidemiology and Molecular Analyses of Influenza B Viruses in Senegal from 2010 to 2019

Influenza virus types A and B are responsible for acute viral infections that affect annually 1 billion people, with 290,000 to 650,000 deaths worldwide. In this study, we investigated the circulation of influenza B viruses over a 10-year period (2010–2019). Specimens from patients suspected of influenza infection were collected. Influenza detection was performed following RNA extraction and real-time RT-PCR. Genes coding for hemagglutinin (HA) and neuraminidase (NA) of influenza B viruses were partially sequenced, and phylogenetic analyses were carried out subsequently. During the study period, we received and tested a total of 15,156 specimens. Influenza B virus was detected in 1322 (8.7%) specimens. The mean age of influenza B positive patients was 10.9 years. When compared to reference viruses, HA genes from Senegalese circulating viruses showed deletions in the HA1 region. Phylogenetic analysis highlighted the co-circulation of B/Victoria and B/Yamagata lineage viruses with reassortant viruses. We also noted a clear seasonal pattern of circulation of influenza B viruses in Senegal.

Epidemiological and Clinical Characteristics of Influenza Outbreaks Among Children in Chongqing, China

Influenza is a global serious public health threat. Seasonal influenza among children in Chongqing has been a heavy health burden. To date, few studies have examined the spatial and temporal characteristics of influenza. This research sheds new light on correlating them with influenza outbreaks with data of over 5 years (2014–2018). All cluster outbreaks among preschool and school-age children reported in Chongqing were collected through the Public Health Emergency Management Information System. The demographical, epidemiological, and clinical data of the cases were analyzed. From 2014 to 2018, a total of 111 preschool- and school-based influenza-like illness outbreaks involving 3,549 cases were identified. Several clinical symptoms that were analyzed in this study showed significant contrast between influenza A and B. Spatial autocorrelation analysis over the 5-year data detected Xiushan district being the most likely cluster. The exploration of the spatial distribution and clinical characteristics of influenza cluster of children in Chongqing could help the effective implementation of health policies. Future studies should be conducted to monitor the outbreaks of influenza among children.

Prevalence and seasonality of viral respiratory infections in a temperate climate region: A 24-year study (1997-2020)

Background

Few long‐term reports have been published on the epidemiology of respiratory viruses despite their frequent involvement in extremely common infections. The aim here was to determine the frequency and distribution of respiratory viruses in a temperate climate area (Barcelona, Spain) throughout a 24‐year period.

Methods

We collected data on all respiratory viruses detected from 1997 to 2020 in our institution. Clinical specimens were analyzed mainly by conventional techniques, and molecular techniques were also used.

Results

Of the 59,579 specimens analyzed, 21,382 (35.9%) were positive for at least one virus. The number of positive samples during cold months was significantly higher than in warm months. Respiratory virus infections were detected in patients of all ages, above all in children under 3 years of age, who were most frequently infected with the respiratory syncytial virus, whereas Influenza A virus predominated in the other groups, especially in adults. A clear demographic and seasonal pattern was established for some viruses. Circulation of other respiratory viruses during the FLUAV H1N1pdm09 and SARS‐CoV‐2 pandemics was observed.

Conclusions

This long‐term study provides new knowledge about the prevalence of respiratory viruses in a Mediterranean region. Throughout the study period, the frequency of some viruses remained constant, whereas others varied with the year. A clear demographic and seasonal pattern was established for some viruses. Patients suffering from severe respiratory infections should be examined for a range of respiratory viruses regardless of gender, age, or season.

DeepFlu: a deep learning approach for forecasting symptomatic influenza A infection based on pre-exposure gene expression

BACKGROUND AND OBJECTIVE

Not everyone gets sick after an exposure to influenza A viruses (IAV). Although KLRD1 has been identified as a potential biomarker for influenza susceptibility, it remains unclear whether forecasting symptomatic flu infection based on pre-exposure host gene expression might be possible.

METHOD

To examine this hypothesis, we developed DeepFlu using the state-of-the-art deep learning approach on the human gene expression data infected with IAV subtype H1N1 or H3N2 viruses to forecast who would catch the flu prior to an exposure to IAV.

RESULTS

The results indicated that such forecast is possible and, in other words, gene expression could reflect the strength of host immunity. In the leave-one-person-out cross-validation, DeepFlu based on deep neural network outperformed the models using convolutional neural network, random forest, or support vector machine, achieving 70.0% accuracy, 0.787 AUROC, and 0.758 AUPR for H1N1 and 73.8% accuracy, 0.847 AUROC, and 0.901 AUPR for H3N2. In the external validation, DeepFlu also reached 71.4% accuracy, 0.700 AUROC, and 0.723 AUPR for H1N1 and 73.5% accuracy, 0.732 AUROC, and 0.749 AUPR for H3N2, surpassing the KLRD1 biomarker. In addition, DeepFlu which was trained only by pre-exposure data worked the best than by other time spans and mixed training data of H1N1 and H3N2 did not necessarily enhance prediction. DeepFlu is available at https://github.com/ntou-compbio/DeepFlu.

CONCLUSIONS

DeepFlu is a prognostic tool that can moderately recognize individuals susceptible to the flu and may help prevent the spread of IAV.

A Novel Recombinant Influenza Virus Neuraminidase Vaccine Candidate Stabilized by a Measles Virus Phosphoprotein Tetramerization Domain Provides Robust Protection from Virus Challenge in the Mouse Model

Current seasonal influenza virus vaccines do not induce robust immune responses to neuraminidase. Several factors, including immunodominance of hemagglutinin over neuraminidase, instability of neuraminidase in vaccine formulations, and variable, nonstandardized amounts of neuraminidase in the vaccines, may contribute to this effect. However, vaccines that induce strong antineuraminidase immune responses would be beneficial, as they are highly protective. Furthermore, antigenic drift is slower for neuraminidase than for hemagglutinin, potentially providing broader coverage. Here, we designed stabilized recombinant versions of neuraminidase by replacing the N-terminal cytoplasmic domain, transmembrane, and extracellular stalk with tetramerization domains from the measles or Sendai virus phosphoprotein or from an Arabidopsis thaliana transcription factor. The measles virus tetramerization domain-based construct, termed N1-MPP, was chosen for further evaluation, as it retained antigenicity, neuraminidase activity, and structural integrity and provided robust protection in vivo against lethal virus challenge in the mouse model. We tested N1-MPP as a standalone vaccine, admixed with seasonal influenza virus vaccines, or given with seasonal influenza virus vaccines but in the other leg of the mouse. Admixture with different formulations of seasonal vaccines led to a weak neuraminidase response, suggesting a dominant effect of hemagglutinin over neuraminidase when administered in the same formulation. However, administration of neuraminidase alone or with seasonal vaccine administered in the alternate leg of the mouse induced robust antibody responses. Thus, this recombinant neuraminidase construct is a promising vaccine antigen that may enhance and broaden protection against seasonal influenza viruses. IMPORTANCE Influenza virus infections remain a high risk to human health, causing up to 650,000 deaths worldwide every year, with an enormous burden on the health care system. Since currently available seasonal vaccines are only partially effective and often mismatched to the circulating strains, a broader protective influenza virus vaccine is needed. Here, we generated a recombinant influenza virus vaccine candidate based on the more conserved neuraminidase surface glycoprotein in order to induce a robust and broader protective immune response against a variety of circulating influenza virus strains.

Influenza B Lineages Have More in Common Than Meets the Eye. Trivalent Influenza Vaccines Trigger Heterotypic Antibodies Against Both Influenza B Viruses

Influenza B is accountable for an important burden during flu epidemics, causing special impact in children and the elderly. Vaccination is the best approach to address influenza infections. However, one of the main problems of this virus is that two different lineages circulate together, Victoria and Yamagata; and trivalent vaccines, that only contain one of these lineages, are still in use. For that reason, if during an epidemic, the lineage not included in the vaccine predominates, a mismatch would occur, and the vaccine effectiveness will be very poor. In this work, we evaluated the cross-protection given by the trivalent Influenza vaccine and compared serological profiles based on age, sex, and the type of vaccine used. We performed a retrospective analysis of serum samples obtained before and after seasonal influenza vaccination during 20 seasons (1998–2018). The results showed that heterotypic reactivity between both influenza B lineages is common, but always lower than the homologous response. Age is a relevant factor for this cross-reactivity between both lineages, while the sex and the type of vaccine not. Vaccination with trivalent influenza vaccines elicits cross-reactive antibodies against both lineages, however, this response might not be enough to provide an appropriate serological protection in case of mismatch.

Synthetic vaccine affords full protection to mice against lethal challenge of influenza B virus of both genetic lineages

A quarter of all seasonal influenza cases are caused by type B influenza virus (IBV) that also dominates periodically. Here, we investigated a recombinant adenovirus vaccine carrying a synthetic HA2 representing the consensus sequence of all IBV hemagglutinins. The vaccine fully protected mice from lethal challenges by IBV of both genetic lineages, demonstrating its breadth of protection. The protection was not mediated by neutralizing antibodies but robust antibody-dependent cellular cytotoxicity and cell-mediated immune responses. Complete protection of the animals required the entire codon-optimized HA2 sequence that elicited a balanced immune response, whereas truncated vaccines without either the fusion peptide or the transmembrane domain reduced the efficacy of protection. Finally, the vaccines did not demonstrate any sign of disease exacerbation following lung pathology and morbidity monitoring. Collectively, these data suggest that it could be worth further exploring this prototype universal vaccine because of its considerable efficacy, safety, and breadth of protection.

Mosaic Hemagglutinin-Based Whole Inactivated Virus Vaccines Induce Broad Protection Against Influenza B Virus Challenge in Mice

Influenza viruses undergo antigenic changes in the immuno-dominant hemagglutinin (HA) head domain, necessitating annual re-formulation of and re-vaccination with seasonal influenza virus vaccines for continuing protection. We previously synthesized mosaic HA (mHA) proteins of influenza B viruses which redirect the immune response towards the immuno-subdominant conserved epitopes of the HA via sequential immunization. As ~90% of current influenza virus vaccines are manufactured using the inactivated virus platform, we generated and sequentially vaccinated mice with inactivated influenza B viruses displaying either the homologous (same B HA backbones) or the heterologous (different B HA backbones) mosaic HAs. Both approaches induced long-lasting and cross-protective antibody responses showing strong antibody-dependent cellular cytotoxicity (ADCC) activity. We believe the B virus mHA vaccine candidates represent a major step towards a universal influenza B virus vaccine.

FluB-RAM and FluB-RANS: Genome Rearrangement as Safe and Efficacious Live Attenuated Influenza B Virus Vaccines

Influenza B virus (IBV) is considered a major respiratory pathogen responsible for seasonal respiratory disease in humans, particularly severe in children and the elderly. Seasonal influenza vaccination is considered the most efficient strategy to prevent and control IBV infections. Live attenuated influenza virus vaccines (LAIVs) are thought to induce both humoral and cellular immune responses by mimicking a natural infection, but their effectiveness has recently come into question. Thus, the opportunity exists to find alternative approaches to improve overall influenza vaccine effectiveness. Two alternative IBV backbones were developed with rearranged genomes, rearranged M (FluB-RAM) and a rearranged NS (FluB-RANS). Both rearranged viruses showed temperature sensitivity in vitro compared with the WT type B/Bris strain, were genetically stable over multiple passages in embryonated chicken eggs and were attenuated in vivo in mice. In a prime-boost regime in naïve mice, both rearranged viruses induced antibodies against HA with hemagglutination inhibition titers considered of protective value. In addition, antibodies against NA and NP were readily detected with potential protective value. Upon lethal IBV challenge, mice previously vaccinated with either FluB-RAM or FluB-RANS were completely protected against clinical disease and mortality. In conclusion, genome re-arrangement renders efficacious LAIV candidates to protect mice against IBV.

Influenza Vaccine Failure Associated With Age and Immunosuppression

BACKGROUND

The influenza vaccine is one of the best ways to prevent influenza infection, but little is known about influenza vaccine failure.

METHODS

This study evaluated patients admitted for acute respiratory illness during 2015-2019 influenza seasons to compare vaccinated influenza-negative to vaccinated influenza-positive patients. Statistical analyses were performed with STATA and R using Pearson χ 2, Kruskal-Wallis, Wilcoxon rank-sum tests, and multivariate logistic regression.

RESULTS

Of 1236 enrolled patients vaccinated for influenza, 235 (19%) tested positive for influenza. Demographics, vaccines, and comorbidities were similar between groups except for morbid obesity (13% influenza negative vs 8%, P = .04), and immunosuppression (63% influenza positive vs 54%, P = .01). Logistic regression analysis demonstrated older patients (odds ratio [OR], 1.47; 95% confidence interval [CI], 1.03-2.10) and immunosuppressed patients (OR, 1.56; 95% CI, 1.15-2.12) were at increased risk for influenza despite immunization. When evaluated by influenza subtype, immunosuppression increased the risk for influenza A/H3N2 (OR, 1.86; 95% CI, 1.25-2.75).

CONCLUSIONS

Our study demonstrated increased risk of influenza vaccine failure in older patients and immunosuppressed patients. These groups are also at increased risk for influenza complications. To improve protection of patients against influenza illnesses, more effective vaccines and strategies are needed.

Influenza Illness and Partial Vaccination in the First Two Years of Life

More information about influenza in low- and middle-income countries could guide the establishment of pediatric influenza vaccine programs. This study (1) characterizes the burden of influenza in infants, and (2) compares signs and symptoms by prior influenza vaccination or influenza illness. Newborns from Managua, Nicaragua, were followed for two years. Data came from primary medical appointments, PCR testing, and parents’ daily symptom diaries. Logistic regression models estimated associations between preceding vaccination or illness and influenza incidence. Linear models compared duration of illness by prior vaccination or influenza illness. Among 833 infants, 31% had PCR-positive influenza, and 28% were vaccinated against influenza. Four (<0.5%) were fully vaccinated. Overall, influenza incidence was 21.0 (95% confidence interval (CI): 18.8, 23.2) per 100 person-years. Incidence was lower among those with prior influenza compared with those without preceding illness or vaccination (OR: 0.64, 95% CI: 0.44, 0.94). Partially vaccinated children had 1 day less fever than those without prior illness or vaccination (p = 0.049). A large proportion of children <2 years in Nicaragua contract influenza. Illness was attenuated for those partially vaccinated. Since few children were fully vaccinated, future studies will need to consider the effectiveness of a two-dose vaccination schedule.

Effectiveness of Trivalent and Quadrivalent Inactivated Vaccines Against Influenza B in the United States, 2011-2012 to 2016-2017

Background

Since 2013, quadrivalent influenza vaccines containing 2 B viruses gradually replaced trivalent vaccines in the United States. We compared the vaccine effectiveness of quadrivalent to trivalent inactivated vaccines (IIV4 to IIV3, respectively) against illness due to influenza B during the transition, when IIV4 use increased rapidly.

Methods

The US Influenza Vaccine Effectiveness (Flu VE) Network analyzed 25 019 of 42 600 outpatients aged ≥6 months who enrolled within 7 days of illness onset during 6 seasons from 2011–2012. Upper respiratory specimens were tested for the influenza virus type and B lineage. Using logistic regression, we estimated IIV4 or IIV3 effectiveness by comparing the odds of an influenza B infection overall and the odds of B lineage among vaccinated versus unvaccinated participants. Over 4 seasons from 2013–2014, we compared the relative odds of an influenza B infection among IIV4 versus IIV3 recipients.

Results

Trivalent vaccines included the predominantly circulating B lineage in 4 of 6 seasons. During 4 influenza seasons when both IIV4 and IIV3 were widely used, the overall effectiveness against any influenza B was 53% (95% confidence interval [CI], 45–59) for IIV4 versus 45% (95% CI, 34–54) for IIV3. IIV4 was more effective than IIV3 against the B lineage not included in IIV3, but comparative effectiveness against illnesses related to any influenza B favored neither vaccine valency.

Conclusions

The uptake of quadrivalent inactivated influenza vaccines was not associated with increased protection against any influenza B illness, despite the higher effectiveness of quadrivalent vaccines against the added B virus lineage. Public health impact and cost-benefit analyses are needed globally.

Correlation of Influenza B Haemagglutination Inhibiton, Single-Radial Haemolysis and Pseudotype-Based Microneutralisation Assays for Immunogenicity Testing of Seasonal Vaccines

Influenza B is responsible for a significant proportion of the global morbidity, mortality and economic loss caused by influenza-related disease. Two antigenically distinct lineages co-circulate worldwide, often resulting in mismatches in vaccine coverage when vaccine predictions fail. There are currently operational issues with gold standard serological assays for influenza B, such as lack of sensitivity and requirement for specific antigen treatment. This study encompasses the gold standard assays with the more recent Pseudotype-based Microneutralisation assay in order to study comparative serological outcomes. Haemagglutination Inhibition, Single Radial Haemolysis and Pseudotype-based Microneutralisation correlated strongly for strains in the Yamagata lineage; however, it correlated with neither gold standard assays for the Victoria lineage.

Airway Delivery of Anti-influenza Monoclonal Antibodies Results in Enhanced Antiviral Activities and Enables Broad-Coverage Combination Therapies

Influenza causes widespread illness in humans and can result in morbidity and death, especially in the very young and elderly populations. Because influenza vaccination can be poorly effective some years, and the immune systems of the most susceptible populations are often compromised, passive immunization treatments using broadly neutralizing antibodies is a promising therapeutic approach. However, large amounts of a single antibody are required for effectiveness when delivered through systemic administration (typically intravenous infusion), precluding the feasible dosing of antibody combinations via this route. The significance of our research is the demonstration that effective therapeutic treatments of multiple relevant influenza types (H1N1, H3N2, and B) can be achieved by airway administration of a single combination of relatively small amounts of three anti-influenza antibodies. This advance exploits the discovery that airway delivery is a more potent way of administering anti-influenza antibodies compared to systemic delivery, making this a feasible and cost-effective therapeutic approach.

Effective and reliable anti-influenza treatments are acutely needed and passive immunizations using broadly neutralizing anti-influenza monoclonal antibodies (bNAbs) are a promising emerging approach. Because influenza infections are initiated in and localized to the pulmonary tract, and newly formed viral particles egress from the apical side of the lung epithelium, we compared the effectiveness of hemagglutinin (HA) stalk-binding bNAbs administered through the airway (intranasal or via nebulization) versus the systemic route (intraperitoneal or intravenous). Airway deliveries of various bNAbs were 10- to 50-fold more effective than systemic deliveries of the same bNAbs in treating H1N1, H3N2, B/Victoria-, and B/Yamagata-lineage influenza viral infections in mouse models. The potency of airway-delivered anti-HA bNAbs was highly dependent on antiviral neutralization activity, with little dependence on the effector function of the antibody. In contrast, the effectiveness of systemically delivered anti-HA bNAbs was not dependent on antiviral neutralization, but critically dependent on antibody effector functions. Concurrent administration of a neutralizing/effector function-positive bNAb via the airway and systemic routes showed increased effectiveness. The small amount of airway-delivered bNAbs needed for effective influenza treatment creates the opportunity to combine potent bNAbs with different anti-influenza specificities to generate a cost-effective antiviral therapy that provides broad coverage against all circulating influenza strains infecting humans. A 3 mg/kg dose of the novel triple antibody combination CF-404 (i.e., 1 mg/kg of each component bNAb) delivered to the airway was shown to effectively prevent weight loss and death in mice challenged with ten 50% lethal dose (LD₅₀) inoculums of either H1N1, H3N2, B/Victoria-lineage, or B/Yamagata-lineage influenza viruses.

IMPORTANCE Influenza causes widespread illness in humans and can result in morbidity and death, especially in the very young and elderly populations. Because influenza vaccination can be poorly effective some years, and the immune systems of the most susceptible populations are often compromised, passive immunization treatments using broadly neutralizing antibodies is a promising therapeutic approach. However, large amounts of a single antibody are required for effectiveness when delivered through systemic administration (typically intravenous infusion), precluding the feasible dosing of antibody combinations via this route. The significance of our research is the demonstration that effective therapeutic treatments of multiple relevant influenza types (H1N1, H3N2, and B) can be achieved by airway administration of a single combination of relatively small amounts of three anti-influenza antibodies. This advance exploits the discovery that airway delivery is a more potent way of administering anti-influenza antibodies compared to systemic delivery, making this a feasible and cost-effective therapeutic approach.

A Decade in Review: A Systematic Review of Universal Influenza Vaccines in Clinical Trials during the 2010 Decade

On average, there are 3-5 million severe cases of influenza virus infections globally each year. Seasonal influenza vaccines provide limited protection against divergent influenza strains. Therefore, the development of a universal influenza vaccine is a top priority for the NIH. Here, we report a comprehensive summary of all universal influenza vaccines that were tested in clinical trials during the 2010-2019 decade. Of the 1597 studies found, 69 eligible clinical trials, which investigated 27 vaccines, were included in this review. Information from each trial was compiled for vaccine target, vaccine platform, adjuvant inclusion, clinical trial phase, and results. As we look forward, there are currently three vaccines in phase III clinical trials which could provide significant improvement over seasonal influenza vaccines. This systematic review of universal influenza vaccine clinical trials during the 2010-2019 decade provides an update on the progress towards an improved influenza vaccine.

Reverse genetics for influenza B viruses and recent advances in vaccine development

Influenza B virus is a respiratory pathogen that affects more severely the pediatric and elderly populations. There are two lineages of influenza B virus that seem to have differential predilection for age groups. Both lineages can co-circulate during the influenza season however one is usually more prominent than the other depending on the season. There are no defined indicators to predict which lineage will dominate in any given season. In recent years, the addition of viruses from both lineages to the seasonal influenza vaccine formulation has improved vaccine protection, although quadrivalent vaccines are not available worldwide. Reverse genetics has facilitated advancements in the field of vaccine development against influenza B virus. Different strategies have been explored showing promising results that could potentially lead to the development broadly protective influenza B virus vaccines.

Quadrivalent cell culture influenza virus vaccine. Comparison to egg-derived vaccine

Influenza virus infections pose a serious public health problem and vaccination is the most effective public health intervention against them. The current manufacture of influenza vaccines in embryonated chicken eggs entails significant limitations. These limitations have been overcome by producing vaccines in cell culture, which allow a faster and more flexible response to potential pandemic threats. Given the impact of influenza B virus on disease burden, the availability of quadrivalent vaccines is useful for increasing the rate of protection from disease. This paper analyzes the limitations of the current production of influenza vaccine in eggs and the advantages of vaccines developed in cell culture, as well as their safety, tolerability, efficacy and effectiveness. Additionally, we reflect on the contribution of new quadrivalent vaccines from cell culture as an alternative in seasonal vaccination campaigns against influenza.

Comparative Severity of Influenza A and B Infections in Hospitalized Children

BACKGROUND

Influenza A viruses are conventionally thought to cause more severe illnesses than B viruses, but few studies with long observation periods have compared the clinical severity of A and B infections in hospitalized children.

METHODS

We analyzed the clinical presentation, outcomes and management of all children <16 years of age admitted to Turku University Hospital, Finland, with virologically confirmed influenza A or B infection during the 14-year period of 1 July 2004 to 30 June 2018. All comparisons between influenza A and B were performed both within predefined age groups (0-2, 3-9 and 10-15 years) and in all age groups combined.

RESULTS

Among 391 children hospitalized with influenza A or B infection, influenza A was diagnosed in 279 (71.4%) and influenza B in 112 (28.6%) children. Overall, there were no significant differences in any clinical features or outcomes, management, treatment at intensive care unit or length of stay between children with influenza A and B, whether analyzed by age group or among all children. As indicators of the most severe clinical presentations, blood cultures were obtained from 101 (36.2%) children with influenza A and 39 (34.8%) with influenza B (P = 0.80), and lumbar puncture was performed to 16 (5.7%) children with influenza A and 11 (9.8%) children with influenza B (P = 0.15).

CONCLUSIONS

The clinical severity of influenza A and B infections is similar in children. For optimal protection against severe influenza illnesses, the use of quadrivalent vaccines containing both lineages of B viruses seems warranted in children.

In Vivo Assessment of Antibody-Dependent Enhancement of Influenza B Infection

A theoretical safety concern proposed in the influenza literature is that therapeutic antiviral antibodies could have the potential for antibody-dependent enhancement (ADE) of infection and disease. ADE may occur when virus-specific antibodies at subtherapeutic, nonneutralizing concentrations facilitate virus uptake and, in some cases, enhance replication, which can lead to an exacerbation of virus-mediated disease. Alternatively, ADE may occur due to antibody-dependent complement activation exacerbating virus-mediated disease in the absence of increased replication. As a result of this theoretical safety concern, safety assessment of anti-influenza antibodies may include an in vivo evaluation of ADE of infection and/or disease. These studies were conducted to investigate the potential of MHAB5553A, a broadly specific, neutralizing therapeutic anti-influenza B antibody, to elicit ADE of infection and disease in mouse models of influenza B infection. In parallel studies, female DBA/2J mice were infected with either influenza B/Victoria/504/2000 or influenza B/Brisbane/60/2008 representing distinct lineages. Assessment of ADE was based on an integration of results from multiple endpoints, including infectious lung viral titers and genomes, body weight, mortality, lung weight, and histopathology. In these studies, the high dose of 15 mg/kg MHAB5553A resulted in substantial attenuation of influenza pneumonia, with more modest effects at 1.5 mg/kg; whereas MHAB5553A treatment at 0.15 or 0.015 mg/kg was generally comparable to vehicle-treated controls. Our results demonstrate that MHAB5553A across a broad range of doses did not enhance primary influenza B infection or disease in this model, and represent a nonclinical de-risking of the ADE potential with this antibody.

Immunogenicity and safety of an inactivated quadrivalent influenza vaccine: a randomized, double-blind, controlled phase III clinical trial in children aged 6-35 months in China

Mismatch between circulating influenza B viruses and vaccine strains occurs frequently. In a randomized, double-blind, controlled phase III clinical study, healthy children aged 6-35 months were randomized into three groups at a ratio of 2:1:1, received two doses of quadrivalent influenza vaccines (QIVs) or licensed trivalent influenza vaccines (TIVs). The primary objective was to evaluate the non-inferiority immunogenicity of QIV compared with the two TIVs, containing B/Victoria or B/Yamagata strain. Safety information was collected for 28 days after each vaccination. Serious adverse events (SAEs) were monitored for 6 months after the second vaccination. A total of 2146 subjects (QIV: 1069, TIV-Vic: 540, TIV-Yam: 537) were enrolled in this study. QIV was found non-inferior to TIVs for shared strains (A/H1N1 and A/H3N2) and corresponding BY strain based on hemagglutination inhibition (HI) antibodies 28 days after the second dose of vaccination. The resulted geometric mean titer (GMT) ratios (QIV/TIV) were 0.98 (0.89, 1.07) for H1N1, 0.95 (0.85, 1.05) for H3N2 and 0.89 (0.81, 0.98) for BY. And the seroconversion rate differences (QIV-TIV) were -0.46% (-3.24%, 2.31%) for H1N1, -1.95% (-5.54%, 1.65%) for H3N2 and -3.58% (-8.11%, 0.95%) for BY. The BV strain in QIV did not reach the non-inferiority criteria, with GMT of 1:52.25 (vs. 1:61.02 of TIV-Vic) and seroconversion rate of 59.49% (vs. 66.85% of TIV-Vic). No increased safety concerns occurred in QIV group. Candidate QIV can provide good protection for children aged 6 to 35 months, and its immunogenicity and safety were proved.

CLINICAL TRIALS REGISTRATION

ClinicalTrials.gov number: NCT03859141.

Estimated hospitalisations attributable to seasonal and pandemic influenza in Australia: 2001- 2013

Background

Influenza continues to cause seasonal epidemics and pandemics in humans. The burden of influenza is underestimated by traditional laboratory-based surveillance, and modelled estimates are required for influenza-attributable morbidity and mortality. We aimed to estimate the influenza-attributable hospitalisation in Australia, by influenza type.

Methods

A generalised-additive regression model was used to estimate type- and age-specific influenza-attributable hospitalisation rates per 100,000 population by principal diagnosis in Australia, from 2001 through 2013. Weekly counts of laboratory-confirmed influenza notifications and by type, influenza A and B were used as covariates in the model. Main principal diagnosis categories of interest were influenza and pneumonia and respiratory admissions. A smoothing spline was used to control for unmeasured time varying factors. Results for 2009, in which the pandemic influenza A(H1N1)pdm09 virus circulated, were not included in annual averages and are reported separately.

Results

During the study period, the estimated annual average, all-age, annual respiratory hospitalisation rates attributable to seasonal influenza type A, B and total influenza were 45.4 (95% CI: 34.9, 55.9), 32.6 (95% CI: 22.8, 42.4), and 76.9 (95% CI: 73.6, 80.2) per 100,000 population, respectively. During 2009, the estimated total pandemic influenza-attributable, all-age, respiratory hospitalisation rate was 56.1 (95% CI: 47.4, 64.9) per 100,000. Older adults (≥85 years of age) experienced the highest influenza-attributable hospitalisation rates for both seasonal and 2009 pandemic influenza. Collinearity between influenza A and B time series in some years limited the ability of the model to resolve differences in influenza attribution between the two virus types.

Conclusion

Both seasonal and pandemic influenza caused considerable morbidity in Australia during the years studied, particularly among older adults. The pandemic hospitalisation rate in 2009 was lower than the average overall annual rate for seasonal influenza, but young to middle aged adults experience a hospitalisation rate similar to that of severe seasonal influenza.

Comparison of antigenic mutation during egg and cell passage cultivation of H3N2 influenza virus

Purpose

When influenza viruses are cultured in eggs, amino acid mutations of the hemagglutinin may occur through egg adaptation. On the other hand, when influenza viruses are cultured in animal cells, no antigenic mutation occurs unlike in eggs. Therefore, we examined whether the antigenic mutations actually occurred after passage of H3N2 (A/Texas/50/2012) virus up to 15 times in eggs and MDCK-Sky3851 cells.

Materials and Methods

Prototype A/Texas/50/2012 (H3N2) influenza virus which was isolated from clinical patient, not passaged in egg, was obtained and propagated using the specific pathogen free egg and the MDCK-Sky3851 cell line up to 15 passage, and the changes in the antigen sequence of the influenza viruses were confirmed by gene sequencing and protein structure analysis.

Results

In term of the hemagglutination titer of influenza virus, the reactivity to chicken and guinea pig red blood cell showed different results between egg propagated and cell propagated viruses. In the sequence analysis results for hemagglutinin and neuraminidase, no antigenic mutation was observed throughout all passages when cultured in MDCK-Sky3851 cells. On the other hand, mutations occurred in three amino acid sequences (H156R, G186S, S219F) in hemagglutinin up to 15 passages when cultured in eggs.

Conclusion

H3N2 influenza virus cultured in eggs could lead mutations in amino acid sequence of hemagglutinin, distinct from the corresponding virus cultured in cells for which no antigenic mutation was observed. These findings suggest that cell culture is a more stable and effective way of production with lower risk of antigenic mutations for the manufacture of influenza vaccines.

Divergent evolutionary trajectories of influenza B viruses underlie their contemporaneous epidemic activity

Two influenza B viruses (Victoria and Yamagata) cocirculate in humans and contribute to the estimated 290,000–650,000 annual influenza-attributed deaths. Here, we analysed influenza B genomic data to understand the causes of a recent surge in human influenza B infections. We found that evolution is acting differently on Yamagata and Victoria viruses and that this has led to the cocirculation of a diverse group of influenza B viruses. If this phenomenon continues, we could potentially witness the emergence of 3 or more distinct influenza B viruses that could require their own vaccine component, thereby complicating influenza vaccine formulation and highlighting the urgency of developing universal influenza vaccines.

Influenza B viruses have circulated in humans for over 80 y, causing a significant disease burden. Two antigenically distinct lineages (“B/Victoria/2/87-like” and “B/Yamagata/16/88-like,” termed Victoria and Yamagata) emerged in the 1970s and have cocirculated since 2001. Since 2015 both lineages have shown unusually high levels of epidemic activity, the reasons for which are unclear. By analyzing over 12,000 influenza B virus genomes, we describe the processes enabling the long-term success and recent resurgence of epidemics due to influenza B virus. We show that following prolonged diversification, both lineages underwent selective sweeps across the genome and have subsequently taken alternate evolutionary trajectories to exhibit epidemic dominance, with no reassortment between lineages. Hemagglutinin deletion variants emerged concomitantly in multiple Victoria virus clades and persisted through epistatic mutations and interclade reassortment—a phenomenon previously only observed in the 1970s when Victoria and Yamagata lineages emerged. For Yamagata viruses, antigenic drift of neuraminidase was a major driver of epidemic activity, indicating that neuraminidase-based vaccines and cross-reactivity assays should be employed to monitor and develop robust protection against influenza B morbidity and mortality. Overall, we show that long-term diversification and infrequent selective sweeps, coupled with the reemergence of hemagglutinin deletion variants and antigenic drift of neuraminidase, are factors that contributed to successful circulation of diverse influenza B clades. Further divergence of hemagglutinin variants with poor cross-reactivity could potentially lead to circulation of 3 or more distinct influenza B viruses, further complicating influenza vaccine formulation and highlighting the urgent need for universal influenza vaccines.

Interplay between cost and effectiveness in influenza vaccine uptake: a vaccination game approach

Pre-emptive vaccination is regarded as one of the most protective measures to control influenza outbreak. There are mainly two types of influenza viruses-influenza A and B with several subtypes-that are commonly found to circulate among humans. The traditional trivalent (TIV) flu vaccine targets two strains of influenza A and one strain of influenza B. The quadrivalent (QIV) vaccine targets one extra B virus strain that ensures better protection against influenza; however, the use of QIV vaccine can be costly, hence impose an extra financial burden to society. This scenario might create a dilemma in choosing vaccine types at the individual level. This article endeavours to explain such a dilemma through the framework of a vaccination game, where individuals can opt for one of the three options: choose either of QIV or TIV vaccine or none. Our approach presumes a mean-field framework of a vaccination game in an infinite and well-mixed population, entangling the disease spreading process of influenza with the coevolution of two types of vaccination decision-making processes taking place before an epidemic season. We conduct a series of numerical simulations as an attempt to illustrate different scenarios. The framework has been validated by the so-called multi-agent simulation (MAS) approach.

Co-circulation of the two influenza B lineages during 13 consecutive influenza surveillance seasons in Italy, 2004-2017

BACKGROUND

Since 1985, two antigenically distinct lineages of influenza B viruses (Victoria-like and Yamagata-like) have circulated globally. Trivalent seasonal influenza vaccines contain two circulating influenza A strains but a single B strain and thus provide limited immunity against circulating B strains of the lineage not included in the vaccine. In this study, we describe the characteristics of influenza B viruses that caused respiratory illness in the population in Italy over 13 consecutive seasons of virological surveillance, and the match between the predominant influenza B lineage and the vaccine B lineage, in each season.

METHODS

From 2004 to 2017, 26,886 laboratory-confirmed influenza cases were registered in Italy, of which 18.7% were type B. Among them, the lineage of 2465 strains (49%) was retrieved or characterized in this study by a real-time RT-PCR assay and/or sequencing of the hemagglutinin (HA) gene.

RESULTS

Co-circulation of both B lineages was observed each season, although in different proportions every year. Overall, viruses of B/Victoria and B/Yamagata lineages caused 53.3 and 46.7% of influenza B infections, respectively. A higher proportion of infections with both lineages was detected in children, and there was a declining frequency of B/Victoria detections with age. A mismatch between the vaccine and the predominant influenza B lineage occurred in eight out of thirteen influenza seasons under study. Considering the seasons when B accounted for > 20% of all laboratory-confirmed influenza cases, a mismatch was observed in four out of six seasons. Phylogenetic analysis of the HA1 domain confirmed the co-circulation of both lineages and revealed a mixed circulation of distinct evolutionary viral variants, with different levels of match to the vaccine strains.

CONCLUSIONS

This study contributes to the understanding of the circulation of influenza B viruses in Italy. We found a continuous co-circulation of both B lineages in the period 2004-2017, and determined that children were particularly vulnerable to Victoria-lineage influenza B virus infections. An influenza B lineage mismatch with the trivalent vaccine occurred in about two-thirds of cases.

Debate on the compositions of influenza B in northern hemisphere seasonal influenza vaccines

Background

Annual influenza vaccination is the most effective way to prevent influenza. Influenza vaccines have traditionally included the hemagglutinins (HA) and neuraminidases (NA) from the two A viruses (H1N1 and H3N2) and either B Yamagata or B Victoria. Mismatches between circulating isolates of influenza B and the vaccines are very common. Taking 2017/2018 winter in northern hemisphere as an example, this study was designed to find out the reasons for mismatch between the trivalent influenza vaccine (TIV) and most of the epidemic isolates at that time, and to discuss if there are some optimized programs for seasonal influenza vaccines.

Methods

HA and NA sequences of the seasonal isolates circulating from December 1, 2017 to February 28, 2018, and in the previously other 7 winters in northern hemisphere from Global Initiative on Sharing All Influenza Data (GISAID) and the influenza database of National Center for Biotechnology Information (NCBI). Phylogenetic trees and genetic distances were constructed or calculated by using MAFFT and MEGA 6.0 software.

Results

Influenza B composition in the TIV recommendation mismatched most of circulating viruses in 2017/2018 winter; the vaccine strain was from the B/Victoria lineage, while most of epidemic isolates were from the B/Yamagata lineage. The epidemic lineage of influenza B reached its peak a little late in the previous winter might be responsible for this mismatch. During 2010-2018, the mean genetic distances between epidemic isolates of influenza A (H1N1 and H3N2) and the vaccines were no higher than 0.02375 ± 0.00341 in both HA and NA. However, concerning influenza B virus, when forecasting done well, the mean genetic distances between epidemic isolates and the vaccines were no higher than 0.02368 ± 0.00272; otherwise, the distances could reach 0.13695 ± 0.00238.

Conclusion

When applying quadrivalent influenza vaccines (QIVs) for vaccination, the recommendations of compositions for influenza B could be altered and assessed once in 3 or 4 years; when economic burden was considered intensively and TIVs were utilized, the recommended compositions for influenza B could be announced in April or May, rather than in February or March as now.

Development and evaluation of a conventional RT-PCR for differentiating emerging influenza B/Victoria lineage viruses with hemagglutinin amino acid deletion from B/Yamagata lineage viruses

BACKGROUND

Recent influenza B/Victoria lineage viruses contain amino acid deletions at positions 162 to 164 of the haemagglutinin (HA) protein. These amino acid deletions have affected the detection of B/Victoria lineage viruses by the lineage-specific conventional reverse-transcription polymerase chain reaction (RT-PCR) that was recommended by World Health Organization (WHO).

OBJECTIVES

We aimed to develop and evaluate a novel lineage-specific RT-PCR for rapid differentiation of the contemporary B/Victoria lineage from B/Yamagata lineage viruses.

STUDY DESIGN

Primers of our in-house RT-PCR were designed to avoid amino acid positions 162 to 164 and to target conserved regions of the HA gene that are specific for B/Victoria and B/Yamagata lineage viruses. Our in-house RT-PCR and WHO RT-PCR were evaluated using influenza B positive clinical specimens or virus culture isolates. Influenza B virus lineage was confirmed by Sanger sequencing.

RESULTS

A total of 105 clinical specimens or virus culture isolates were retrieved, including 83 with B/Victoria lineage and 22 with B/Yamagata lineage viruses. Our in-house RT-PCR correctly identified B/Victoria lineage viruses in all 83 samples, including 82 samples with double or triple amino acid deletion in the HA protein. Conversely, the WHO lineage-specific conventional RT-PCR failed to detect any of the 82 samples with HA amino acid deletions. For the 22 samples with B/Yamagata lineage viruses, both RT-PCR assays have correctly identified B/Yamagata lineage in all samples.

CONCLUSIONS

Our novel lineage-specific RT-PCR has successfully detected all contemporary B/Victoria lineage viruses with amino acid deletions in HA. This protocol is especially useful for laboratories without the equipment for real-time PCR.

Spatial, Temporal and Genetic Dynamics Characteristics of Influenza B Viruses in China, 1973-2018

Annual influenza B virus epidemics and outbreaks cause severe influenza diseases in humans and pose a threat to public health. China is an important epidemic area of influenza B viruses. However, the spatial, temporal transmission pathways and the demography history of influenza B viruses in China remain unknown. We collected the haemagglutinin gene sequences sampled of influenza B virus in China between 1973 and 2018. A Bayesian Markov chain Monte Carlo phylogeographic discrete approach was used to infer the spatial and temporal phylodynamics of influenza B virus. The Bayesian phylogeographic analysis of influenza B viruses showed that the North subtropical and South subtropical zones are the origins of the Victoria and Yamagata lineage viruses, respectively. Furthermore, the South temperate and North subtropical zones acted as transition nodes in the Victoria lineage virus dispersion network and that the North subtropical and Mid subtropical zones acted as transition nodes in the Yamagata lineage virus dispersion network. Our findings contribute to the knowledge regarding the spatial and temporal patterns of influenza B virus outbreaks in China.

Immunogenicity and safety of a quadrivalent inactivated influenza vaccine in pregnant women: a randomized, observer-blind trial

Vaccination against influenza during pregnancy provides direct protection to pregnant women and indirect protection to their infants. Trivalent inactivated influenza vaccines (IIV3s) are safe and effective during pregnancy, but quadrivalent inactivated influenza vaccines (IIV4s) have not been evaluated in pregnant women and their infants. Here, we report the results of a randomized phase IV study to evaluate the immunogenicity and safety of IIV4 vs. IIV3 in pregnant women. Participants aged ≥18 years at weeks 20 to 32 of gestation were randomly assigned in a 2:1 ratio to receive a single dose of IIV4 (n = 230) or IIV3 (n = 116). Between baseline and 21 days after vaccination, hemagglutination inhibition (HAI) antibody titers increased in both groups by similar magnitudes for the two influenza A strains and single B strain common to IIV4 and IIV3. For the additional B strain in IIV4, HAI titers were higher in IIV4 recipients than IIV3 recipients (post-/pre-vaccination geometric mean titer ratio, 6.3 [95% CI: 5.1 − 7.7] vs. 3.4 [95% CI: 2.7 − 4.3]). At delivery, in both groups, HAI antibody titers for all strains were 1.5 − 1.9-fold higher in umbilical cord blood than in maternal blood, confirming active transplacental antibody transfer. Rates of solicited and unsolicited vaccine-related adverse events in mothers were similar between the two groups. Live births were reported for all participants and there were no vaccine-related adverse events in newborns. These results suggest IIV4 is as safe and immunogenic as IIV3 in pregnant women, and that maternal immunization with IIV4 should protect newborns against influenza via passively acquired antibodies.